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Tech Article

BMW E30 3-Series Idling Problems Related to Air Flow Meter or Not

Last Updated: 10/29/2016

Parts Group: Air flow meter

This article discusses the air flow meter (a.k.a. mass air flow sensor), for the E30 with the main focus being on its role, if any, in the idling of the car. If you're not here for the technical analysis but would rather buy a used unit from us, guaranteed to work and fit, then please select the link below:

A friend of mine is reassembling the fuel injection system on his E30 after working on the engine.

It’s having issues idling. One possible suspect might seem to be the air flow meter since it’s so fundamental to how the fuel injection system works. So, he removed the part from my E30 and took it home to try it on his own car.

On a hunch, I tried to start my own E30 even with the air flow meter removed. It started and idled just fine.

Bottom line: the air flow meter seems to be immaterial to whether or not the car can idle well or at all. Why might this be?

I figure that the L-Jetronic type of fuel injection, or the superset thereof, the Motronic system, has two modes: idle and non-idle. This is controlled by a master switch called the throttle position sensor. It is attached to the throttle spindle: It senses whether or not the throttle pedal is being pushed down to any extent, and it puts voltage to a wire, or not. It’s a simple yes-or-no situation.

When it senses that the throttle isn’t being pushed down, the fuel injection system goes into idle mode. This means certain components (for example, the idle control valve) are active, and others (for example, the air flow meter) are not. When the throttle pedal is depressed, the system exits idle mode, and it reverses which components are active.

On these assumptions, a problem with idling is either due to a component relevant to idling (including those that are supposed to maintain vacuum) or in the throttle control system that selects idle mode -- or not.